User manual

DodoSim 206 FSX User Manual

Page 69

4.2 EMERGENCY PROCEDURES

4.2.1 Auto-Rotation

Auto-rotation enables a helicopter to safely land when the engine is no longer driving the rotor blades

due to either failure of the engine, transmission system, or an intentional reduction of engine power by

the pilot, (for the purpose of practicing emergency landings.)

During an auto-rotation the up-flow of air through the main rotor causes it to continue turning like a

windmill and thus provides enough lift for a controlled descent, much like a sycamore seedpod falling

from a tree. The pilot must manage rotor RPM using the collective pitch lever, applying small amounts

of pitch to prevent the rotor from over-speeding whilst ensuring that too much pitch does not cause

enough drag to slow the rotor. If the rotor RPM decays much below the green arc then it may be

impossible for the up-flow to regain rotor RPM, further RPM is lost and the helicopter will plummet.

The ideal airspeed for an auto-rotation is 55 knots. The pilot should use cyclic pitch to maintain the

airspeed and collective pitch to control the rotor RPM. With practice it should be possible to balance the

two and achieve the ideal 1,500 feet per minute descent rate.

As the helicopter nears the ground, the forward airspeed should be arrested using aft cyclic input and

the helicopter brought into a low hover, at which time the pilot must apply collective pitch to cushion the

touchdown. As the pilot applies collective, the increased drag and sudden loss of up-flow will cause the

rotors to slow dramatically. If this is performed too high above ground, rotor speed will be lost and the

helicopter will descend to the ground too fast, as all lift is lost.

Hint: “Run-on” auto-rotations are easier to perform, whereby a small amount of forward airspeed is

maintained all the way until touchdown. This forward airspeed helps reduce rotor RPM decay as the

pilot performs the final increase in collective pitch to arrest the descent.

Important note: Due to the sycamore “windmilling” effect, it is possible for a helicopter to perform a

vertical auto-rotation. However, this is not possible in FSX due to inherent shortcomings in Microsoft’s

core helicopter aerodynamics programming that it has currently proved impossible to overcome.

Therefore, it is recommended that run-on auto-rotations be performed and collective pitch reduced as

airspeed decays below 20 knots in order to avoid the main rotor stall that will otherwise inevitably and

unfortunately occur.

55 Knots IAS

100% NR

Auto-rotation attitude

1,500 fpm descent rate